AL.com reported that Etowah County sheriff's deputies were called to McDonald's home around 7:20 p.m. Saturday for reports of a shooting. They found Sparks lying dead in the side yard.
McDonald and his wife were the only people at the home with Sparks at the time of the killing.
Sparks' coworkers at First Action Plumbing Services in Anniston addressed his death Sunday on Facebook.
"All of us at First Action Plumbing are saddened and shocked at the untimely, unfortunate and senseless death of our employee, co-worker and friend Doug Sparks," the statement read. "The details of what took place last night are still very unclear. Please join us in support and prayer for his wife, children, family and friends."
Sparks' widow, Diana Sparks, wrote on social media that he was and always will be the love of her life.
"He had a big heart and loved everyone, especially his family," she wrote. "I love you always and forever."
Diana Sparks shared a private message her husband sent her on their January anniversary, in which he thanked her for a wonderful life together and said she would always be his greatest love.
"I love you so much, hope you have a great anniversary," Doug Sparks wrote. "In my eyes, you will always be the best wife ever."
He ended the note by saying she made him the “happiest person in the world.”
Sparks is survived by his wife, five children, his parents, a brother, and several grandchildren, according to his obituary.
"He was a loving husband, father, brother, uncle and friend that would do anything for his family and friends and will be greatly missed," the obituary read.
Detectives learned that the McDonalds had hired Sparks to repair a clogged sink a week before the shooting, AL.com said. McDonald, who did not know Sparks prior to that job, then hired him to replace the plumbing at the house, authorities said.
Sparks had been working on that job most of the day Saturday and the McDonalds even fed the man, Etowah County Sheriff Jonathon Horton said.
"Shortly after arriving home, which was just, you know, within an hour of the incident occurring, (McDonald) had fixed the gentleman a sandwich," Horton told WBRC. "And he appears to have been eating that sandwich at the time of the shooting."
McDonald, who has no criminal record, told investigators he does not remember the shooting or what may have preceded it, Horton told AL.com.
McDonald’s wife was on the front porch of the home when she heard gunshots. She did not see the killing, the news site reported.
"It's a mystery," Horton said.
Investigators have seized home surveillance footage, hoping it will shed light on what took place.
McDonald remained jailed Thursday morning.